I don't understand what role Lucas should have according to you?
the trial will never take place, because it would be narratively very boring, useless for Tybalt if not as a spite. but even if there was a real complaint, the only aspect in which Lucas' testimony could have value is on the issue of the fire, but Tybalt would have to be a real idiot to include it in the charges, it is one thing to tell it to Jill to look like a hero, it is another thing to write it down in a complaint (if he did he would surely be assisted by a lawyer). If the complaint was about damaging the Preps' property and jeopardizing the fundraiser (entering a party uninvited is a minor charge and also difficult to prove), Lucas would have no weight.
the only other aspect in which Lucas could bring his testimony is about the slap to Tybalt, but we are talking about an optional event that doesn't seem to have had big consequences.
there are characters who are given a name and a face just to enrich the "scenography" but they don't play any role
